Method and apparatus for locating faults in electrical cable systems



May 19, 1925. 1,538,383

W. R. BU LLARD METHOD AND APPARATUS FOR LOCATING FAULTS IN ELECTRICALCABLE SYSTEMS Original Filed Noy. 25, 192

INVENTOR' 1 MP5 //ar-a ATTORNEY Patented May 19, 1925.

UNITED sTA Es 1,538,383 PATENT OFFICE.

WILLIAM RALPH :BULLARD, on NEW YORK, N. Y.

METHOD AND APPARATUS FOR LOCA'IING FAULTS IN ELECTRICAL CABLE SYSTEMS.

Original application filed November 25,1922, Serial No. 603,818. Dividedand this application filed November 14, 1923. Serial No. 674,624.

To all whom it may concern:

Be it known that I, WILLIAM RALPH BUL- LARD, a citizen of the UnitedStates of America, residing at 63 West 183rd Street,

in the county of Bronx,-city and State of New York, have inventedMethods and Apparatus for Locating Faults in Electrical Cable Systems,of which the following is a specification.

This application relates to a novel method and system or apparatus fordetecting the presence of currents flowing in electrical transmissioncables and locating faults therein.

This application is a division ofmy application Serial No. 603,318,filed November25,

The object of my invention generally is to obviate certain defectsandinaccuracies of the prior systems forlocating faults, and particularly anovel method and system which may be used supplementaryto orindependently of other systems in vogue to locate the faults withgreater accuracy and certainty than has hitherto been possible.

For a better understanding of the novel features and principle of myinvention and the best mode or modes in which I contemplate applying thesame, reference may be had to the accompanying drawings where- Fig. 1 isa diagrammatic view illustrating one embodiment of the fault locatingsystem;. 1

Fig. 2 is a view illustrating in more detail the generator fieldcircuit;

Fig. 3 is a view illustrating further details of the generator, and

Fig. 4 illustrates a modified interrupting switch.

The drawings present more. or less diagrammatically the preferredembodiment of my perfected method and system for locating faults incables, the'perfected method and system havmg been arrlved at afterextended experiments with various alternative arrangements. This methodconsists generally in supplying intermittently andperiodically a directcurrent. herein called the tracing current, through the faulty cable andcausing it to pass outwardly through the fault or ground. andapproximating the relative position of the'fault by applying to thecable at points removed from. the point r of application of the tracingcurrent a de- 'tector (for example, similar to that illustrated inFig. 1) which is responsive to the periodic tracing current, Ordinarilythe fault or ground may be quite accurately located by comparatively feweliminating tests. 'As it is only necessary to detect the absence orpresence of the tracing current any suitable detecting element may beused in the place of the measuring instrument 8 illustrated in Fig. 1,such for example as a sound or telephone detector which I have found byexperiment to give fair results in certain cases. In this case thearmature 14 will be provided with collecting rings instead of acommutator.

According to prior methods either an alternating or rapidly pulsatingcurrent has been used as the tracing current-with audible indicatingapparatus, or else direct current with a crude method of indication suchas a compassheld in the vicinity of the cable.

.My invention has the advantages of great sensitivity,comparative-freedom from disturbance due to external fields, visualindication (which is much more. reliable than audible indication) andother advantages which will be described hereinafter.

Methods using alternating or rapidly pulsating current are unreliableunless the fault has practically zero resistance to ground, for if thefault has resistance then an alternating or pulsating potential willexist between the cable conductor and ground, causing current to flowbeyond the fault due to cable capacity, thereby giving false indication.The use of direct current eliminates tlfils; effect and renders theindication relia le.

Another difiiculty which is often encountered in locating faults byprior methods is the fact that sometimes the tracing. current does notpass directly into the ground at x the fault but travels for-somedistance along the cable sheath (when the cable has a metallic sheath)in either or both directions from the fault before passing into theground. Such conditions can be readily detected by the use of myinvention.

Referring to Fig. 1, my system or apparatus includes a generator 5 whichis adapted to be connected to a detecting or measuring device 8, andwhose field poles are excited by the magnetism set up by the currentflowing in a conductor 1, the construction and arrangement being such,

as hereinafter set forth, that when the generator 5 is mechanicallyoperated or rotated the current or E. M. F. generated and indicated bythe instrument 8 is substantially proportional to the volume of currentflowing in the conductor 1. 4 is a ring or magnetic circuit of soft ironwhich forms the field of the generator 5. 4 is in two parts, these partsbeing joined by a hinge at 6 and provided with a catch or clasp at 7.The object of this construction is to permit encircling the cable, 1,with the field 4 without breaking the continuity of the cable. Thegenerator 5 may be designed to furnish either alternating or rectifiedcurrent at its terminals. This current is carried by small conductors 2,3 to the measuring instrument 8 which may be of the moving coilgalvanometer type in case rectified current is furnished at theterminals of the generator 5. The coils 10 are in magnetic relationshipwith the field 4 and are supplied with current from the battery 11through the rheostat 12 and connections 9. The circuit arrangement andtherelationship of these coils are such that the resultant magnetism ofboth coils can be varied continuously from a maximum in one direction toa maximum in the opposite direction by adjusting the rheostat 12. Whennot in use 7 the battery circuit is broken in the usual manner. Thegenerator 5 is provided with some means of revolving the armature 14between the pole pieces, 15. This may be a hand operated crank 16 or anyother suitable source of mechanical power. A constant speed clutch 17may be provided, if desired, for keeping the speed of the armatureapproximately constant with varying speeds atthe crank 16.

It is assumed for illustrative purposes that the cable has a fault at 22which fault is caused because of the connection of one ductors at oneend of the cable, the other terminal of the generator being grounded.

The current thus passes through the cable to the fault, through thefault to ground and thence through the ground back to the generator.

The hand generator 5 is moved from one location to another along thecable and by embracing the cable with it at each location it enables thedetection of the presence or absence of the direct or tracing currentflowing through the cable to the fault. This is done by rotating thearmature by a crank or other means and noting the deflection of thecurrent detecting instrument 8., The purpose of the interrupter 20 inthe D. C. circuit is to enable the operator of the device to distinguishbetween the current flowing through the cable to the fault, and anystray current which may be flowing in the sheath of the cable. Theperiod of interruption is preferably'very slow, as for example onesecond on and one second off, which is found to reduce the capacityeffect to a negligible quantity. Another disturbing influence may becurrent flowing in the vicinity of the instrument which may give asufficiently powerful field to affect the indication.

It can readily be seen that in order to locate the fault it is onlynecessary to take readings at a sufficient number of points along thecable. When the point 28 is reached there will be no deflection of theinstrument 8, indicating that the fault has been passed.

In locating faults in cables having metallic sheaths it is sometimesdesirable for more accurate work to devise some means for eliminating orminimizinz the efiect of sheath currents on the detecting apparatus andthen take successive readings on the instrument 8 with the effect of thesheath E. M. F. or current thereon modified in amount for comparativepurposes. I will now describe an effective method of accomplishing this.

Referring again to Fig. 1, 32 represents a conductor of low resistancewhich can be readily connected to the cable sheath by the clamps 29 forforming a low resistance path for sheath current around the detectinginstrument 5. The switch 30 is inserted in this circuit. The method ofusing this arrangement is as follows: A reading is taken at theinstrument 8 with the switch 30 open, giving a periodic deflection dueto the current supplied to the cable from the generator 23. A secondreading 15 taken with the switch 30 closed and it is noted whether thedeflection in this case is more or less than with the switch 30 open. Ifit is more the instrument 5 is indicating the difference betweenconductor current and sheath current and is located between thesourceof' supply 23 and the fault 22. If it is less the instrument isindicating sheath current only and is located at a point on the cablebeyond the fault. This method usually need only be used after the faulthas been localized in a comparatively small portion of'the cable byusing the instrument 5 without the shunting conductor 32. The latter isthen used in the final tests to determine the exact location of thefault.

When the fault hasbeen located in thisv manner, a final and accuratecheck on what has been determined can be efiected by entirelyeliminating the sheath current by cut ting rings out of the sheath onopposite sides of the place where the fault has been located, it beingpossible to replace the lead sheath withoutdisturbing the insulation ormaking a new joint in case there was an error in the location, and ifthere was no error then only the faulty section has been cut.

If the fault should consist of a breakdown of insulation between two ormoreconductors and not between any one conductor and the sheath orground, this device can be used to locateafaultof this kind in themanner described above except that the generator 23 has its terminalsconnected to the faulty conductors and that in this case the cableis-not completely encircledby.

the field circuit.- Instead the field circuit is opened sufiiciently sothat the cable can be placed just halfway within the gap at the openingof the field. The device is then swung radially around the cable untilthe point of maximumdeflection is found.

The sensitivity of the device is limited only by the design of theinstrument 5 and that of the detecting instrument 8. The combination canbe easily constructed to indicate the presence, of direct current of theorder of a smallfraction of an ampere. In practice a limitation isimposed by the disturbing effects of stray fields and stray currents inthe sheath... If these fields or ourrents are constant then they can beeliminated by means of the neutralizing circuit 9. In using theneutralizing device, the procedure is toclose the circuit of battery 11and turn the crank before the field 4 has been clamped or, positionedaround the cable and then to adjust the variable resistance until thedetecting or indicating instru- With ment 8 reads zero or substantiallyso. this adjustment made, the field 41 is positioned around the cableand another reading then taken with the tracing current flowing throughthe fault. The instrument should then indicate correctly the presence oftracing current flowing past the generator. If the stray fields orcurrents are varying with variations giving deflections of theinstrumentS less than those due to the tracing current their presence isnot important. However, if the disturbing variations in the deflectionof the instrument 8 are larger than those due to the tracing current itmay become impossible to distinguish between tracing current and thestray fields, or currents without modifying.

period of the interrupter 26 equal to that of the instrument 8, theperiodic deflection of the latter can be multiplied many times therebyminimizing the effect of disturbing variations of stray fields orcurrents and enabling the operator of the device to readily distinguishbetween the deflection due to these and that dueTo the tracing current.

The period of the instrument may be adjusted by changing the length ofthe spring or by adjusting the weights toward or away from the pivot ofthe moving element or by some other similar means. Constant speed forthe interruption may be obtained by using a synchronous motor drive.

The indications of the instrument may be further amplified by replacingthe interrupter 26 with a reversing switch which will reverse thetracing current on the instrument and thereby render the detectingapparatus more sensitive. Such a revers-. ing switch is indicateddiagrammatically in Fig. 4 at 20 wherein the supply circuit includingthe generator 23 and the variable resistance element 24: is periodicallyconnected with the cable and the ground so as to reverse the polarity ofthe current thereto at each make and break of the interrupter 26, theground connection being illustrated conventionally and the circuitleading to the cable 1 being indicated at 36. The connections aresimilar to the usual connections of a double pole double throw reversingswitch, the supply circuit being reversibly connected with the upper andlower sets of contacts 37 and 38 and the receiving circuit beingconnected, as indicated, with the upper and lower switch elements 38 and39 so that reverse polarities are obtained by closing the switchelements alternately.

The instrument 8 preferably has its zero point in the center of thescale, and the neutralizing rheostat is adjusted to bring the averageindication of the needle in the neighborhood of the zero point when thenormal tracing current is flowing.

In the case of direct current power circuits, it is not usuallypracticable to make any test for detecting faults while any substantialpower current is flowing because of the tendency of the magnetismproduced by the power current to overpower any tracing current inmagnetizing the field of the generator. In the case of alternating powercircuits, however, it is ordinarily practicable to detect the fault inthe manner herein described, notwithstanding that large power currentsare flowing; but in testing for faults on such circuits it is importantthat the field of the generator 5 surrounds all the conductors in orderto avoid errors due to the passage of tracing current throughtransformers or other apparatus connected to the circuit.

The armature 14 may be equipped with a two segment commutator 14 therebygiving a pulsating unidirectional current through" the instrument andthese segments may be, if desired, of a large diameter as compared tothe width of brush surface, thereby to minimize the effect of changes inradial position with respect to the axis of the pole pieces of thegenerator. This has the further advantage that within certain ranges an.increase of surface speed at the commutator tends to steady the contactresistance. I sistance may be minimized by making the impedance of thetotal meter circuit high as compared to the contact resistance. Theserefinements in accuracy of measurement and others including a higharmature reactance compared to the resistance of instrument 8, thegovernor type speed regulator 17, and the non-magnetic gaps 40 in thefield circuit 4 with the field having a substantially larger diameterthan the cable and spaced therefrom by means of the spacers 39 and moreparticlularly set forth in the aforesaid application which is directedto the measurement of the volume of current flowing.

I claim:

1. The method of locating faults in cables, which consists in causing aslowly varying unidirectional current to pass through the faulty cable,causing magnetism produced by said current to excite the field magnet ofa generator detector first at one point along the cable and then atanother, and noting the presence or absence of the generated current atdifferent points along the cable.

2. The method of locating faults in cables which consists in supplyingintermittently through the cable at definite prolonged intervals aunidirectional current and causing it to pass out through the faultyportion of the cable and positioning an electric generator with itsfield magnetically associated with the cable at different points thereoffor testing for the magnetic fields set up about the cable correspondingto the intermittent unidirectional current passing therethrough.

3. The method of locating faults in cables which consists in supplyingintermittently through the faulty cable at definite prolonged intervalsa unidirectional current and causing it to pass out the faulty point ofthe cable and positioning an electric generator at different pointsalong the suspect; ed cable with its field magnetically associated withthe field set up about the cable The effect of varying contact re-' bythe-unidirectional current and detecting the character of the magneticfield about the cable by the, character of the currents generated by thegenerator when operated.

at. The method of locating faults in a faulty cable which consists inconnecting therewith a direct current source with one side connected tothe cable and the other side connected to the ground and intermittentlyinterrupting the direct current supply circuit at definitely controlledintervals and positionin a mechanically operated generator at difierentpoints throughout the cable with its field magnetically associated withthe fields set up by the cable and thereby causing the generator torespond to the presence of the magnetic fields set up about the cable bythe intermittent unidirectional current when the generator is at a pointpast which the intermittent unidirectional current flows in the cable.

5. The method of locating grounds in a metallic sheath cable whichconsists in supplying to the faulty cable a varying unidirectionalcurrent and causing it to pass out through the faulty point of the cableto set that point, and placing a short circuiting shunt about the pointof application of the generator and taking readings of the generatorwith this shunt both open and closed. 6. In a system for locating afault in a cable, the combination of a magnetic path or circuit, meansfor opening and closing the magnetic circuit so as to surround a cableor conductor carrying direct current with said magnetic circuits, arevoluble armature adjacent to and in magnetic relation with saidmagnetic circuit, means for revolving said armature, a detecting deviceconnected to said armature, means for circulating direct current throughthe cable or conductor to a fault existing in said cable or conductor,and means for periodically interrupting this direct current.

7. In a system for locating a fault in a cable, the combination of amagnetic path or circuit of suitable reluctance, means for mechanicallysurrounding a cable or conductor with said magnetic path, a separateelectric circuit adjacent to and in magnetic connection with themagnetic path, a source of direct current supply connected to saidseparate electric circuit and means for varying volving the saidarmature, a detecting device connected to said armature, meansforcirculating direct current through the conductor or cable to a faultwhich may exist on this conductor or cable, and means for periodicallyinterrupting this direct current.

8. In a system for locating a fault in a cable, the combination of amagnetic path or circuit of low reluctance, means for opening andclosing the magnetic circuit so as to surround a cable or conductor withsaid magnetic circuit, a revoluble armature adjacent to and in magneticrelation with said magnetic circuit, means for revolving said armature,an indicating device, having a free natural period of oscillation, andconnected to said armature, means for circulating direct current throughthe cable or conductor to a fault which may exist on said cable orconductor, and means for periodically interrupting this direct currentwith a period corresponding to the natural period of the indicatingdevice.

9. In a system for locating a fault in a cable, the combination of amagnetic path or circuit of low reluctance, means for mechanicallysurrounding a cable or conductor carrying direct current with themagnetic path without breaking the continuity of the direct currentcircuit, a separate electric circuit adjacent to and in magneticconnection with magnetic path, a source of direct current 'supplyconnected to said separate electric circuit and means for varying thecurrent flowing in this circuit, a revoluble armature adjacent to andforming a part of the magnetic circuit, means for revolving saidarmature, an indicating device,having a free natural period ofoscillation connected to said armature, means for circulating directcurrent through the cable or conductor to a fault which may exist onsaid cable or conductor, and means for periodically interrupting thisdirect current with a period corresponding to the natural period of theindicating instrument;

10. The method of locating a fault in a metallic sheath cable whichconsists in passing through the faulty'cable an intermittent tracingcurrent, positioning a device responsive to the magnetism set up by thetracing current at a point removed from-the point of application of theintermittent tracing current, and then observing successive responses onthe device with the effect of the sheath current thereon modified inamount by alternately connecting and disconnecting a sheath shunt aboutthe responsive device.

11. The method of locating a fault in a metallic sheath cable whichconsists in passing through the faulty cable a slowly varyingunidirectional current, positioning a device responsive to the magnetismset up by the tracing current at difierent points along the faulty cableand then with the sheath current alternately shunted past and away fromthe responsive device, taking successive readings thereon to obesrve.the effect-of the sheath current thereupon.

12. The method of locating grounds in a metallic sheath cable whichconsists in supplying to the faulty cable a varying unidirectionalcurrent and causing it to pass out through the faulty point of the cableto set up about the cable a magnetic field corresponding to the varyingunidirectional current, positioning a device at different points alongthe faulty cable which is responsive to the tracing current and thesheath current, placing a short-circuiting shunt about the point ofapplication of the responsive device and then observing the responsethereon with the shunt both open and closed.

13. The method of locating faults in cables which consists in supplyingintermittently through the cable at definite prolonged in-. tervals, andwith a reversed polarity at each successive interval, a unidirectionalcurrent and causing it to pass out through the faulty portion of thecable and positioning an electric generator with its field magneticallyassociated with the cable at diflerent points thereof for testing forthe magnetic fields set up about the cable corresponding to theintermittent unidirectional current passing therethrough.

In testimony whereof, I have signed my name to this specification.

WILLIAM RALPH BULLARD.

